Plating of aluminum



Patented 2 9,

* UNITED ,S'lATES aPA'lEN-T OFFICE,

. shame or summon Leonhard Pernen-Be'rlin, vested in tlie Alien Property No Drawing. Application was 2:, 1m, 's erial No. 252,503. In Germany August 2. 1931 Y Claims. 01. 117-130) The present invention relates to a process for mined the nature of my said-invention and in the production of firmly adherent metal coatings on objects of aluminum or aluminum alloys, in

which the coatings are obtained solely by dipping the objects in suitable metal-salt solutions. According to the invention an aqueous solution of metal-fluoride compounds and in particular an aqueous solution of metal-silicon-fiuoride or metal-boron-fluoride is proposed for this purp se. The saidsalts of metals which are nobler than aluminum are suitable.

In order on one hand to hinder the hydrolysis of the dissolved salts and on the-other to improve the deposition of the metal in question on to the objects, it is insome circumstances of advantage to add fluorides oi the alkali, light or heavy metals, in particular the fluor-silicates or fluorborates, to the solution. To improve the metal coating still further and in particular to obtain a fine-crystalline structure of the layer, it has been found advantageous to add to the bath organic wh'atmanner thesameis'tobe clare that what I claim is:

1. A non-electrolytic process for the produc-" tion ora firmly adherent coating of a pure heavy metal, which is nobler than aluminum and which forms a water-soluble silicon-fluoride andlor boron-fluoride, on objects of aluminum oraluminum alloys, in which the objects are merely immersed in an aqueous solution of a member ,0!

performed 1' dethe group consisting of the'silicon-fiuoride's and boron-fluorides of said heavy metal until a coating of the latter is termed, the immersion being continued until a pure metallic coating of a thickness or the order of about 0.1 him. has been produced. r 2. A non-electrolytic process for the production of a firmly adherent of a pure heavy metal, whichis nobler than aluminum'and which orms a water-soluble silicon-fluoride and/or ron-fiuoride, on objects or aluminum or aluminum alloys, in which the objects are merely immersed in an aqueous. solution of a silicon-fluorrelatively thick coatings can be obtained by the process, the coatings-are well adapted for polish- Ezanpl 1 An almost saturated cadmium-silicon fiuoride solution is diluted with four to five volumes of ide oi the said heavy metal until a coating of the latter is formed, the immersion being continued until a pure metallic coating .oi a thickness oi the order of about 0.1 mm has been produced.

3. A non-electrolytic process for the production of a firmly adherent coating of a pure heavy metal, which is nobler-than aluminumand which forms a water-soluble silicon-fluoride and/or boron-fluoride, on objects oi aluminum or aluminum alloys; in which the objects are merel immersed in an aqueous solution or a boron-fluoride oi the said heavy metal until a coating of the I Y latter is formed, the immersion'beingcontinu'ed until a puremetallic coating of .a thickness of water, One or two or the abovementioned colloids are added tov the solution in the proportion of. two to five parts per "thousand of the total solution. The work pieces to be treated are dipped in this solution for five to ten minutes at room temperature.

Example 2 An almost saturated solution; of zinc-boron- 1 fiuoride is diluted with iour to five volumes of water. Additions of a heavy metal'fiuoride say oi the metal nickel, iron, copper or tin in the pr0- portion of about two, per thousand and of a colloid in the proportion of about five per thousand of the total liquid, follow. The solution is used at about 30 f0 40 C.

' Having now Particularly. described a ascerthe order or about 0.1 mnnhas been produced.

.4. A non-electrolytic process for the produc-- tion of a firmly adherent coating of a -eheavy metal. which is nobler than aluminum and which forms a water-soluble silicon-fluoride and/or boron-fluoride. on objects of aluminum or aluminumnlloys, in which the objects are merely immersed in an aqueous solution oi a silicon-fluoride of the said heavymetal until a coating'oi the latter is formed, said solution containing a colloid selected from the sl'omzo oi' gelatin,

selatoses, albumoses, dextrlneand sulphite-lye,"

the immersion being continued until a pure metallic coating of a thickness or the order oi about 0.1 mm'. hasbeen'produced.

5. A non-electrolytic process for the produc .tionoiafirmlyadherentcoatingoiapureheavy metal, which is nobler and which forms a water-soluble silicon-fluoride and/or boron-fluoride, on objects of aluminum or aluminum alloys, in which the objects are merely im-V mersed in an aqueous solution of a boron-fluoride of the said heavy metal until a coating of the latter is formed. said solution containing a colloid selected from the group consisting of gelatin, gelatoses, albumoses, dextrine and sulphite-lye, the immersion being continued until a pure metallic coating of a thickness of the order of about 0.1 mm. has been produced.

6. A process according to claim 1, wherein the concentration of the aqueous solution is that corresponding to a saturated solution of the heavy metal silicon-fluoride or boron-fluoride which has been diluted with about 4-5 volumes of water.

7. A process according to claim 2, wherein the concentration of the aqueous solution is that corresponding to a saturated solution of the heavy. 20

has been diluted with about 4-5 volumes of water.

8. A process according to claim 3, wherein the concentration of the aqueous solution is that corresponding to a saturated solution of the heavy metal silicon-fluoride or boron-fluoride which has been diluted with about 4-5 volumes of water.

9. A process according to claim 4, wherein the concentration 01 the aqueous solution is that corresponding to a saturated solution of the heavy metal silicon-fluoride or boron-fluoride which has been diluted with about 4-5 volumes of water. I

10. A process according to claim 5, wherein the concentration otthe aqueous solution is that corresponding to a saturated solution of the heavy metal silicon-fluorid or boron-fluoride which has been diluted with about 4-5 volumes of water.

LEONHARD PERNER. 

